This invention is concerned with starting circuits for high power discharge lamps, and more particularly, with a starter circuit for a high power metal iodide discharge lamp.
Starter circuits for discharge lamps may be differently designed. Since the lamp is generally series connected to an inductor, the latter may be provided with an intermediate output and connected in order to constitute an auto-transformer and, thus, to increase the starting voltage applied to the lamp.
However, it has been found that the corresponding apparatus is undesirably heavy, combersome and expensive, and cannot operate if it is located quite far from the corresponding lamp.
Another kind of starter circuit is, for instance, described in the French Pat. No. 2 280 289. This circuit includes a thyristor the starting angle of which is modified as the line voltage. However, such a circuit generates undesired transient currents before it generates the useful impulse and, thus, wastes energy.
It is known that to start a 2000 Watt discharge lamp, the circuit must generate an impulse having a peak voltage which is at least 1100 Volts and a has duration greater than 100 microseconds, as measured at 900 Volts.